Preparation and Characterization of Polyurethane Microcapsules for Controlled Release of Bendiocarb

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Abstract
In this study, waterborne polyurethane (WPU) microcapsules encapsulating bendiocarb were successfully prepared by interfacial polymerization for sustainable mosquito control. A high encapsulation efficiency of 94% was achieved by systematically optimizing the emulsifier concentration (2% PVA), core-to-wall ratio (1:2), reaction temperature (50°C), and reaction time (6 h). Comprehensive characterization confirmed the uniform spherical morphology (particle size 1–3 µm), core-shell structure, and thermal stability of the microcapsules. Importantly, a core-to-wall ratio threshold of 2:1 was determined: microcapsules with core-to-wall ratios ≤ 2:1 have a dense cross-linked network that provides dual core protection (physical barrier + thermal dissipation; initial decomposition temperature T₀ ≥ 163°C), while ratios > 2:1 lead to shell discontinuities and thermal channeling (T₀ ≤ 145°C), and the protective effect of the walls on the core is lost. Long-term efficacy of the microencapsulated fabrics was demonstrated by bioassays: 27% residual drug retention after 20 washes and the drug residue after 28 days of cumulative release (at a constant temperature of 40°C) was 30.8%. This study establishes an ecologically sound framework for the targeted application of pesticides based on the World Health Organization guidelines on pesticide residues.

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